For several years, I've figured there wasn't much point in running my own mailserver anymore. Almost all hosting companies these days can provide the basics (smtp, imap, spam filtering, backups). All was going well until I was forced into it again last year when the hosting provider I had just moved to screwed everything up - I needed a solution quickly, and so I ended up sharing a Slicehost with a friend. This worked out well - Slicehost have a great product offering! - but it still meant more maintenance headaches for me... configuring spamassassin, adding accounts, hearing complaints about the slow web interface, worrying about backups or accidentally taking the server down...
Moving to Google Apps (something I never thought I'd do 2 years ago!) has been in the cards for several months now. They offer everything we need and more for free. It will take some getting used to - for example, I inevitably end up joining umpteen mailing lists, and like to filter them... until I came across karltk's post on Filtering on List-Id in Gmail I was really second-guessing my decision... there's also the oddity in 'archiving' mail (ie: moving it out of the inbox) and giving something a 'label' (ie: sticking it in a folder). These are arguably more advanced ways of working with email, but you still need to change the way you think, which I'm sure will confuse some users.
The saving grace is that you can use the same old mail reader you've used for donkey's years, and use it like you always have. What's more, the web-interface is great.
The only thing I'm worried about is uptime... hopefully we won't see many more outages in the future. Still, it is a free service after all.